1. Field of the Invention
This invention relates to a pressure swing adsorption system, and, more particularly, to an oxygen concentrator system and method of operating same having a multi-chamber canister for receiving compressed air from a compressor and directing the air through a series of chambers integral within a single assembly for producing concentrated oxygen in a pressure swing adsorption system.
2. Description of Related Art
Adsorption separation processes depend on the ability of certain solids to selectively adsorb one or more components from a gaseous mixture. In oxygen concentrators for patient use, the adsorption separation processes are usually fixed bed operations, including two main steps, the adsorption step and the desorption step.
Pressure Swing Adsorption (PSA) is a useful technique for separating components of gaseous mixtures in such medical uses. A gaseous mixture, typically ambient air, is fed into a chamber, where the components are separated, producing a stream with a high percentage of one component. Air contains many components, namely approximately 21% oxygen, 78% nitrogen, 0.9% argon and 0.1% other trace gases. PSA can be used to separate the oxygen from the inlet air, to supply the patient with higher concentrations of oxygen.
Generally, such component separation in the chamber is achieved by using a zeolite, or molecular sieve, which has a selective affinity for adsorbing a certain component in the mixture. Zeolites are natural or synthetically produced molecular sieves that have uniform pores or crystalline cavities. Chemical components small enough to fit into the zeolite's pores are adsorbed onto the surface of the zeolite material. How readily a component adsorbs onto the zeolite depends on the shape and size of the molecule compared to the shape and size of the pores in the zeolite pellet. A zeolite can absorb a molecule of any diameter up to its own pore size.
Pressure Swing Adsorption relies on swings in pressure to cycle the chamber sequentially from selective adsorption to desorption. This swing can occur from high pressure to atmospheric pressure or from atmospheric pressure to vacuum. If the swing occurs from atmospheric pressure to vacuum, it is technically considered Vacuum Pressure Swing Adsorption (VPSA). It is well known to those of skill in the art the PSA and VPSA techniques for component separation are quite different, each technique with its own attendant benefits and deficiencies.
A typical pressure swing adsorption system is an oxygen concentrator that separates the oxygen from air for subsequent inhalation by a patient. Conventional systems provide between 0.5 liters per minute (LPM) and 10 LPM. Such oxygen concentrators include a plurality of molecular sieve beds for separating the gas into an oxygen and a nitrogen fraction whereby the oxygen is subsequently provided to a patient while the nitrogen is retained in the sieve bed and subsequently purged. These oxygen concentrators include several components such as an air compressor, two three-way air valves, multiple canisters each housing a separate molecular sieve and a product reservoir tank. Such structures require extensive valving and plumbing which affects the efficiency and costs of these systems.
Some PSA systems of the prior art include a multi-chamber canister for a pressure swing adsorption system which includes at least three chambers. The canister includes a housing of a general length. A first molecular sieve chamber is disposed within the housing for receiving a first molecular sieve for separating air from the ambient environment into a concentrated gas component. At least a second molecular sieve-chamber is also disposed within the housing for receiving a second molecular sieve for separating air from the ambient environment into a concentrated gas component. A supply chamber is disposed within the housing for receiving air from the ambient environment and for communicating the air to either the first or second molecular sieve chamber.
While many conventional systems are capable of delivering sufficient flow rates to meet the patient's need, they do not meet many of the patients' demands including the desire for high efficiency, high product gas concentrations, and low weight. For example, many of the conventional systems require a significant amount of molecular sieve materials and power to operate. Other systems provide oxygen at insufficient purities at certain flow rates. Some conventional systems have implemented features and methods which attempt to address some of these insufficiencies.
For example, U.S. Pat. No. 6,683,256 (“the '256 patent”) discloses a molecular sieve type gas separation apparatus that alters the duration of the desorption regeneration phase and the adsorption generation phase according to the desired concentration of product gas. More particularly, the '256 patent discloses an adaptive control method for a gas separation apparatus that uses an oxygen sensor responsive to the concentration constituent of the product gas. Based on the data received from the oxygen sensor, the gas separation apparatus can modify the duration of the adsorption generation phase and the desorption regeneration phase. If the sensor indicates that the concentration constituent of the product gas is higher than desired, then the desorption phase can be shortened and thus the requirements for the supply of input gas can be decreased.
Similarly, U.S. Pat. No. 5,906,672 (“the '672 patent”) discloses an oxygen concentrator that incorporates a microprocessor to evaluate the output of product gas from the oxygen concentrator. Additionally, the device provided includes a closed-loop feedback circuit to evaluate the durations of the phase of the pressure swing adsorption cycle. The microprocessor instructs the device to incrementally increase the valve timing until a decrease in oxygen output is sensed. When a decrease in oxygen output is detected, the microprocessor instructs the device to step back to the previous timing.
U.S. Pat. No. 4,627,860 (“the '860 patent”) discloses a oxygen concentrator and test apparatus. The '860 patent teaches using a microprocessor to monitor the sensing functions and performance of various components of the concentrator. Furthermore, the '860 patent teaches a test apparatus in communication with the concentrator to display the selected monitored functions of the concentrator. The test apparatus allows the operator to monitor the performance levels of the machine and diagnose component problems.
U.S. Pat. No. 5,474,595 (“the '595 patent”) discloses a pressure swing adsorption apparatus with a capacity control system for the compressor. The capacity control system provides a mechanical valve within the housing of the unit which can be manually set to restrict the intake of ambient air into the compressor. The restricted quantity of ambient air reduces the load on the compressor and thus the power consumed by the system.
While the systems of the prior art are suitable for their intended purposes, they are not capable of delivering a reliable oxygen concentration of 90% or more at 5 LPM in a system with minimal weight, size, sound level and power consumption characteristics. Furthermore, the prior art does not describe a device which is capable of generating the maximum oxygen concentration purity possible for flow rates from 0 to 5 LPM. Moreover, the prior art does not teach a system capable of operating at minimum power requirements at flow rates from 0 to 5 LPM. Additionally, the prior art does not teach a system capable of operating in both a low power mode and an increased oxygen mode. It is to such an oxygen concentration system that the present invention is primarily directed.